Also receive this, when trying to archive a large directory:

[ 2055.147509] INFO: task z_wr_iss_h:2169 blocked for more than 120 seconds.
[ 2055.154450]       Tainted: P         C OE     5.4.0-1018-raspi #20-Ubuntu
[ 2055.161401] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2055.169403] z_wr_iss_h      D    0  2169      2 0x00000028
[ 2055.169420] Call trace:
[ 2055.169441]  __switch_to+0x104/0x170
[ 2055.169453]  __schedule+0x30c/0x7c0
[ 2055.169462]  schedule+0x3c/0xb8
[ 2055.169470]  io_schedule+0x20/0x58
[ 2055.169483]  rq_qos_wait+0x100/0x178
[ 2055.169492]  wbt_wait+0xb4/0xf0
[ 2055.169502]  __rq_qos_throttle+0x38/0x50
[ 2055.169514]  blk_mq_make_request+0x128/0x610
[ 2055.169526]  generic_make_request+0xb4/0x2d8
[ 2055.169537]  submit_bio+0x48/0x218
[ 2055.169779]  vdev_disk_io_start+0x670/0x9f8 [zfs]
[ 2055.170005]  zio_vdev_io_start+0xdc/0x2b8 [zfs]
[ 2055.170229]  zio_nowait+0xd4/0x170 [zfs]
[ 2055.170451]  vdev_mirror_io_start+0xa8/0x1b0 [zfs]
[ 2055.170673]  zio_vdev_io_start+0x248/0x2b8 [zfs]
[ 2055.170896]  zio_execute+0xac/0x110 [zfs]
[ 2055.170937]  taskq_thread+0x2f8/0x570 [spl]
[ 2055.170950]  kthread+0xfc/0x128
[ 2055.170960]  ret_from_fork+0x10/0x1c
[ 2055.170990] INFO: task txg_quiesce:2380 blocked for more than 120 seconds.
[ 2055.178025]       Tainted: P         C OE     5.4.0-1018-raspi #20-Ubuntu
[ 2055.184958] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2055.192949] txg_quiesce     D    0  2380      2 0x00000028
[ 2055.192963] Call trace:
[ 2055.192984]  __switch_to+0x104/0x170
[ 2055.192995]  __schedule+0x30c/0x7c0
[ 2055.193003]  schedule+0x3c/0xb8
[ 2055.193046]  cv_wait_common+0x188/0x1b0 [spl]
[ 2055.193082]  __cv_wait+0x30/0x40 [spl]
[ 2055.193310]  txg_quiesce_thread+0x27c/0x380 [zfs]
[ 2055.193349]  thread_generic_wrapper+0x74/0xa0 [spl]
[ 2055.193370]  kthread+0xfc/0x128
[ 2055.193381]  ret_from_fork+0x10/0x1c
[ 2055.193438] INFO: task smbd:3662 blocked for more than 120 seconds.
[ 2055.199853]       Tainted: P         C OE     5.4.0-1018-raspi #20-Ubuntu
[ 2055.206784] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2055.214772] smbd            D    0  3662   3498 0x00000000
[ 2055.214786] Call trace:
[ 2055.214800]  __switch_to+0x104/0x170
[ 2055.214810]  __schedule+0x30c/0x7c0
[ 2055.214818]  schedule+0x3c/0xb8
[ 2055.214856]  cv_wait_common+0x188/0x1b0 [spl]
[ 2055.214892]  __cv_wait+0x30/0x40 [spl]
[ 2055.215121]  zil_commit_impl+0x234/0xd30 [zfs]
[ 2055.215344]  zil_commit+0x48/0x70 [zfs]
[ 2055.215567]  zfs_read+0x2f8/0x418 [zfs]
[ 2055.215831]  zpl_read_common_iovec+0xa8/0x110 [zfs]
[ 2055.216065]  zpl_read_common+0x4c/0x70 [zfs]
[ 2055.216288]  zpl_xattr_get_dir+0x10c/0x128 [zfs]
[ 2055.216519]  zpl_xattr_get+0xcc/0x1a8 [zfs]
[ 2055.216742]  zpl_xattr_user_get+0x68/0x90 [zfs]
[ 2055.216764]  __vfs_getxattr+0x60/0x80
[ 2055.216774]  vfs_getxattr+0x140/0x160
[ 2055.216784]  getxattr+0x9c/0x2c0
[ 2055.216794]  path_getxattr+0x7c/0xd0
[ 2055.216805]  __arm64_sys_getxattr+0x28/0x38
[ 2055.216815]  el0_svc_common.constprop.0+0x80/0x218
[ 2055.216823]  el0_svc_handler+0x34/0xa0
[ 2055.216833]  el0_svc+0x10/0x2cc
[ 2055.216858] INFO: task borg:5639 blocked for more than 120 seconds.
[ 2055.223265]       Tainted: P         C OE     5.4.0-1018-raspi #20-Ubuntu
[ 2055.230193] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2055.238179] borg            D    0  5639   4001 0x00000000
[ 2055.238193] Call trace:
[ 2055.238208]  __switch_to+0x104/0x170
[ 2055.238218]  __schedule+0x30c/0x7c0
[ 2055.238226]  schedule+0x3c/0xb8
[ 2055.238267]  cv_wait_common+0x188/0x1b0 [spl]
[ 2055.238303]  __cv_wait+0x30/0x40 [spl]
[ 2055.238530]  zil_commit_impl+0x234/0xd30 [zfs]
[ 2055.238752]  zil_commit+0x48/0x70 [zfs]
[ 2055.238975]  zfs_write+0xa3c/0xb90 [zfs]
[ 2055.239197]  zpl_write_common_iovec+0xac/0x120 [zfs]
[ 2055.239419]  zpl_iter_write+0xe4/0x150 [zfs]
[ 2055.239471]  new_sync_write+0x100/0x1a8
[ 2055.239480]  __vfs_write+0x74/0x90
[ 2055.239489]  vfs_write+0xe4/0x1c8
[ 2055.239505]  ksys_write+0x78/0x100
[ 2055.239514]  __arm64_sys_write+0x24/0x30
[ 2055.239524]  el0_svc_common.constprop.0+0x80/0x218
[ 2055.239532]  el0_svc_handler+0x34/0xa0
[ 2055.239541]  el0_svc+0x10/0x2cc
[ 2055.239555] INFO: task kworker/u8:3:35327 blocked for more than 120 seconds.
[ 2055.246754]       Tainted: P         C OE     5.4.0-1018-raspi #20-Ubuntu
[ 2055.253681] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2055.261670] kworker/u8:3    D    0 35327      2 0x00000028
[ 2055.261715] Workqueue: writeback wb_workfn (flush-zfs-1)
[ 2055.261728] Call trace:
[ 2055.261740]  __switch_to+0x104/0x170
[ 2055.261750]  __schedule+0x30c/0x7c0
[ 2055.261758]  schedule+0x3c/0xb8
[ 2055.261798]  cv_wait_common+0x188/0x1b0 [spl]
[ 2055.261834]  __cv_wait+0x30/0x40 [spl]
[ 2055.262059]  zil_commit_impl+0x234/0xd30 [zfs]
[ 2055.262284]  zil_commit+0x48/0x70 [zfs]
[ 2055.262509]  zpl_writepages+0xec/0x170 [zfs]
[ 2055.262522]  do_writepages+0x58/0x108
[ 2055.262534]  __writeback_single_inode+0x48/0x438
[ 2055.262543]  writeback_sb_inodes+0x234/0x560
[ 2055.262553]  __writeback_inodes_wb+0x50/0xe8
[ 2055.262562]  wb_writeback+0x2ac/0x3c8
[ 2055.262571]  wb_workfn+0x464/0x528
[ 2055.262582]  process_one_work+0x1d0/0x430
[ 2055.262591]  worker_thread+0x54/0x4a0
[ 2055.262601]  kthread+0xfc/0x128
[ 2055.262612]  ret_from_fork+0x10/0x1c
[ 2055.262725] INFO: task z_wr_iss_h:59659 blocked for more than 120 seconds.
[ 2055.269739]       Tainted: P         C OE     5.4.0-1018-raspi #20-Ubuntu
[ 2055.276638] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2055.284594] z_wr_iss_h      D    0 59659      2 0x00000028
[ 2055.284600] Call trace:
[ 2055.284609]  __switch_to+0x104/0x170
[ 2055.284614]  __schedule+0x30c/0x7c0
[ 2055.284618]  schedule+0x3c/0xb8
[ 2055.284622]  io_schedule+0x20/0x58
[ 2055.284627]  rq_qos_wait+0x100/0x178
[ 2055.284631]  wbt_wait+0xb4/0xf0
[ 2055.284635]  __rq_qos_throttle+0x38/0x50
[ 2055.284641]  blk_mq_make_request+0x128/0x610
[ 2055.284646]  generic_make_request+0xb4/0x2d8
[ 2055.284650]  submit_bio+0x48/0x218
[ 2055.284752]  vdev_disk_io_start+0x670/0x9f8 [zfs]
[ 2055.284844]  zio_vdev_io_start+0xdc/0x2b8 [zfs]
[ 2055.284940]  zio_nowait+0xd4/0x170 [zfs]
[ 2055.285030]  vdev_mirror_io_start+0xa8/0x1b0 [zfs]
[ 2055.285125]  zio_vdev_io_start+0x248/0x2b8 [zfs]
[ 2055.285214]  zio_execute+0xac/0x110 [zfs]
[ 2055.285235]  taskq_thread+0x2f8/0x570 [spl]
[ 2055.285241]  kthread+0xfc/0x128
[ 2055.285246]  ret_from_fork+0x10/0x1c
[ 2175.981513] INFO: task z_wr_iss_h:2169 blocked for more than 241 seconds.
[ 2175.988451]       Tainted: P         C OE     5.4.0-1018-raspi #20-Ubuntu
[ 2175.995404] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2176.003407] z_wr_iss_h      D    0  2169      2 0x00000028
[ 2176.003423] Call trace:
[ 2176.003445]  __switch_to+0x104/0x170
[ 2176.003456]  __schedule+0x30c/0x7c0
[ 2176.003465]  schedule+0x3c/0xb8
[ 2176.003473]  io_schedule+0x20/0x58
[ 2176.003486]  rq_qos_wait+0x100/0x178
[ 2176.003494]  wbt_wait+0xb4/0xf0
[ 2176.003505]  __rq_qos_throttle+0x38/0x50
[ 2176.003517]  blk_mq_make_request+0x128/0x610
[ 2176.003529]  generic_make_request+0xb4/0x2d8
[ 2176.003540]  submit_bio+0x48/0x218
[ 2176.003783]  vdev_disk_io_start+0x670/0x9f8 [zfs]
[ 2176.004009]  zio_vdev_io_start+0xdc/0x2b8 [zfs]
[ 2176.004233]  zio_nowait+0xd4/0x170 [zfs]
[ 2176.004454]  vdev_mirror_io_start+0xa8/0x1b0 [zfs]
[ 2176.004677]  zio_vdev_io_start+0x248/0x2b8 [zfs]
[ 2176.004900]  zio_execute+0xac/0x110 [zfs]
[ 2176.004941]  taskq_thread+0x2f8/0x570 [spl]
[ 2176.004954]  kthread+0xfc/0x128
[ 2176.004965]  ret_from_fork+0x10/0x1c
[ 2176.004994] INFO: task txg_quiesce:2380 blocked for more than 241 seconds.
[ 2176.012027]       Tainted: P         C OE     5.4.0-1018-raspi #20-Ubuntu
[ 2176.018957] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2176.026958] txg_quiesce     D    0  2380      2 0x00000028
[ 2176.026973] Call trace:
[ 2176.026996]  __switch_to+0x104/0x170
[ 2176.027006]  __schedule+0x30c/0x7c0
[ 2176.027018]  schedule+0x3c/0xb8
[ 2176.027058]  cv_wait_common+0x188/0x1b0 [spl]
[ 2176.027094]  __cv_wait+0x30/0x40 [spl]
[ 2176.027320]  txg_quiesce_thread+0x27c/0x380 [zfs]
[ 2176.027359]  thread_generic_wrapper+0x74/0xa0 [spl]
[ 2176.027419]  kthread+0xfc/0x128
[ 2176.027430]  ret_from_fork+0x10/0x1c
[ 2176.027490] INFO: task smbd:3662 blocked for more than 241 seconds.
[ 2176.033906]       Tainted: P         C OE     5.4.0-1018-raspi #20-Ubuntu
[ 2176.040838] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2176.048826] smbd            D    0  3662   3498 0x00000000
[ 2176.048840] Call trace:
[ 2176.048854]  __switch_to+0x104/0x170
[ 2176.048864]  __schedule+0x30c/0x7c0
[ 2176.048872]  schedule+0x3c/0xb8
[ 2176.048910]  cv_wait_common+0x188/0x1b0 [spl]
[ 2176.048946]  __cv_wait+0x30/0x40 [spl]
[ 2176.049173]  zil_commit_impl+0x234/0xd30 [zfs]
[ 2176.049395]  zil_commit+0x48/0x70 [zfs]
[ 2176.049660]  zfs_read+0x2f8/0x418 [zfs]
[ 2176.049895]  zpl_read_common_iovec+0xa8/0x110 [zfs]
[ 2176.050119]  zpl_read_common+0x4c/0x70 [zfs]
[ 2176.050350]  zpl_xattr_get_dir+0x10c/0x128 [zfs]
[ 2176.050572]  zpl_xattr_get+0xcc/0x1a8 [zfs]
[ 2176.050802]  zpl_xattr_user_get+0x68/0x90 [zfs]
[ 2176.050818]  __vfs_getxattr+0x60/0x80
[ 2176.050828]  vfs_getxattr+0x140/0x160
[ 2176.050843]  getxattr+0x9c/0x2c0
[ 2176.050854]  path_getxattr+0x7c/0xd0
[ 2176.050864]  __arm64_sys_getxattr+0x28/0x38
[ 2176.050874]  el0_svc_common.constprop.0+0x80/0x218
[ 2176.050882]  el0_svc_handler+0x34/0xa0
[ 2176.050891]  el0_svc+0x10/0x2cc
[ 2176.050917] INFO: task borg:5639 blocked for more than 241 seconds.
[ 2176.057327]       Tainted: P         C OE     5.4.0-1018-raspi #20-Ubuntu
[ 2176.064262] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2176.072254] borg            D    0  5639   4001 0x00000000
[ 2176.072267] Call trace:
[ 2176.072281]  __switch_to+0x104/0x170
[ 2176.072292]  __schedule+0x30c/0x7c0
[ 2176.072299]  schedule+0x3c/0xb8
[ 2176.072339]  cv_wait_common+0x188/0x1b0 [spl]
[ 2176.072375]  __cv_wait+0x30/0x40 [spl]
[ 2176.072601]  zil_commit_impl+0x234/0xd30 [zfs]
[ 2176.072824]  zil_commit+0x48/0x70 [zfs]
[ 2176.073047]  zfs_write+0xa3c/0xb90 [zfs]
[ 2176.073270]  zpl_write_common_iovec+0xac/0x120 [zfs]
[ 2176.073493]  zpl_iter_write+0xe4/0x150 [zfs]
[ 2176.073544]  new_sync_write+0x100/0x1a8
[ 2176.073552]  __vfs_write+0x74/0x90
[ 2176.073561]  vfs_write+0xe4/0x1c8
[ 2176.073578]  ksys_write+0x78/0x100
[ 2176.073588]  __arm64_sys_write+0x24/0x30
[ 2176.073598]  el0_svc_common.constprop.0+0x80/0x218
[ 2176.073606]  el0_svc_handler+0x34/0xa0
[ 2176.073615]  el0_svc+0x10/0x2cc